The prior art closest to the invention pertains to a system for the synchronization of multimedia streams in real time. A patent document EP 1775964 A1 (Huawei Technologies Co. Ltd. “Method and device for stream synchronization of real-time multimedia transport over packet network”) describes a prior-art system of this kind.
This patent document has a solution for synchronizing two multimedia streams (in this case an audio stream and a video stream) traveling through the Internet.
The proposed solution relies on the addition of two buffers, one for the audio stream and one for the video stream. The invention presented in this patent enables dynamic evaluation of the size of these buffers. To this end, the invention evaluates the time of transfer of each stream by taking the difference between the sending instant and the reception instant and deduces a transfer time therefrom. This difference is then used to define the size of the different buffers.
However, this technique has several drawbacks.
A first drawback lies in the fact that the mechanism described in this document uses two buffer memories of variable size, necessitating temporary storage space to manage these buffers.
A second drawback lies in the fact that the solution described in these documents calls for the implementation of systematic temporary storage of all the frames received. This induces the addition of supplementary latency in addition to that inevitably induced by the traversal of the Internet.
A third drawback lies in the fact that the measurement of the difference of propagation time is done by the difference of mean propagation times measured for each stream (by difference between the instant of sending and the instant of reception). This technique calls for the transmission of a time-stamp generally encoded on four bytes, thus introducing additional overhead (or extra bit rate).